The present invention relates generally to flat panel displays and more particularly to flat panel displays with gettering systems which assist in evacuating and maintaining the evacuation of flat panel displays.
Cathode-ray tube (CRT) displays have been the predominant display technology for purposes such as home television and computer systems. For many applications, CRTs have advantages in terms of superior color resolution, high contrast and brightness, wide viewing angles, fast response times, and low manufacturing costs. However, CRTs also have major drawbacks such as excessive bulk and weight, fragility, high power and voltage requirements, strong electromagnetic emissions, the need for implosion and x-ray protection, undesirable analog device characteristics, and a requirement for an unsupported vacuum envelope that limits screen size.
To address the inherent drawbacks of CRTs, alternative display technologies have been developed. These technologies generally provide flat panel displays, and include liquid crystal displays (LCDs), both passive and active matrix, electroluminescent displays (ELDs), plasma display panels (PDPs), vacuum fluorescent displays (VFDs) and field emission displays (FEDs).
The FED offers great promise as an alternative flat panel display technology. Its advantages include low cost of manufacturing as well as the superior optical characteristics generally associated with the CRT display technology. Like CRTs, FEDs are phosphor based and rely on cathodoluminescence as a principle of operation. FEDs rely on electric field or voltage induced emissions to excite the phosphors by electron bombardment rather than the temperature induced emissions used in CRTs. To produce these emissions, FEDs have generally used row-and-column addressable cold cathode emitters of which there are a variety of designs, such as point emitters (also called cone, microtip, or xe2x80x9cSpindtxe2x80x9d emitters), wedge emitters, thin film amorphic diamond emitters, and thin film edge emitters.
Each of the FED emitters is typically a miniature electron gun of micron dimensions. When a sufficient voltage is applied between the emitter and an adjacent gate, electrons are emitted from the emitter into a vacuum which is located between a baseplate, upon which the emitters are mounted, and a faceplate having a transparent anode surface to which the phosphors are applied. The emitters are biased as cathodes and the emitted electrons are attracted and accelerated to strike the phosphors on the anode surface. The phosphors then emit visible light which form picture elements, or pixels, which make up the images on the face of the FED.
Electron emissions in FEDs require a hard vacuum to avoid serious problems, such as vacuum degradation, emission current degradation, and/or plasma generation or ionization which can lead to non-uniform brightness of the display or shortening of the working life of the display.
The FED is conventionally hermetically sealed in air and then evacuated through a tube which is pinched or melted shut after evacuation in a process called xe2x80x9ctubulationxe2x80x9d. To assist in the evacuation process and to maintain the hard vacuum, a xe2x80x9cgettering materialxe2x80x9d is used which absorbs contaminant gases by various chemical reactions. There are basically two different types of gettering materials. One type is an evaporable gettering material, which is capable of being deposited by an evaporative deposition process. The other type is a non-evaporable gettering material, which is formed into the configuration in which it will be used. Non-evaporable getters are manufactured in various geometries, such as metal wires or strips covered by a porous coating of gettering material.
One approach of using an evaporable gettering material is to deposit it in the portion of the tube between the flat panel display and the pinch or melt point of the tubulation process. This has the disadvantage of the tube being accidentally broken off during the handling which accompanies manufacturing.
Another approach is simply forming an evaporable getter at a location along the interior surface of baseplate or/and faceplate. This is disadvantageous because a getter typically needs a substantial amount of surface area to perform the gas collection function. However, it is normally important that the ratio of active display area to the overall interior surface area be quite high in an FED. Because an evaporable getter is formed by evaporative deposition, a substantial amount of inactive area along the interior surface of the baseplate or/and the faceplate structure would normally have to be allocated for a getter, thereby significantly reducing the active-to-overall area ratio. In addition, the active components of the FED easily become contaminated during the gettering material deposition process and some of the active FED components could become short-circuited.
A non-evaporable getter is an alternative to an evaporable getter. A non-evaporable getter typically consists of a pre-fabricated unit. As a result, the likelihood of damaging the components of an FED during the installation of a non-evaporable getter into the FED is considerably lower than with an evaporable getter. While a non-evaporable getter does require substantial surface area, the pre-fabricated nature of a non-evaporable getter generally allows it to be placed closer to the actual display elements than an evaporable getter.
For flat panel displays with both these gettering systems, it has been determined that certain gases remain and are difficult to remove by the gettering system even after long periods of time. Knowing that the contaminant gases cause severe problems, those skilled in the art have long sought a system by which the gettering effect could be improved, but they have been unsuccessful.
The present invention provides a flat panel display having a cathode carrying baseplate hermetically sealed to an anode-coated, phosphor-bearing, faceplate with a vacuum between the baseplate and the faceplate. Electron emitters are mounted on the baseplate in contact with the cathode and a gettering material is disposed in a housing open to the vacuum and adjacent to the baseplate. The gettering material is conductively connected to the cathode on the baseplate to charge the gettering material to attract contaminant gas ions so that they can be absorbed by the gettering materials to maintain the vacuum.
The present invention provides a flat panel display having a cathode carrying baseplate hermetically sealed to an anode-coated, phosphor-bearing, faceplate. A vacuum is located between the baseplate and the faceplate. Electron emitters connected to the cathode are mounted on the baseplate and a gettering material is disposed in a housing open to the vacuum and adjacent to the faceplate. The gettering material is conductively connected to the cathode on the baseplate by a conductive connection which extends outside the vacuum to allow checking the quantity of residual gas ions present in the vacuum.